Switch contact



R. A. WAITE SWITCH CONTACT Dec. 22, 1936.

Filed Aug. 27. 1935 F: G. 5 7 WW WWW INVENTOR/ v ATTORNEY Gil PatentedDec. 22, 1936 NlTED STATES PATENT OFFICE 2.964.998 swrrcn comuc'rApplication August 27, 1935, Serial No. 38,011

1 Claim.

This invention relates to electric contacts and to the method ofmanufacture of such contacts.

Contacts in electric circuits are subject to wear due in part to burningcaused by the arcing which occurs as a circuitis made and broken. Worncontacts require replacement at intervals according to the rate of wear,which depends upon the particular service required of such contacts.Such replacements involve considerable expense in time and materials. Ithas been found that by using a copper contact having a cadmium insert asone of a pair ofcontacts the wear thereon caused by arcing has beenminimized, especially when used in cooperation with a cadmiumimpregnated carbon contact. For example, with a certain switch having acopper contact cooperating with a carbon contact, the life of the carboncontact was about three months and that of the copper contact about sixmonths in commercial operation. Upon replacing the carbon contact with acadmium impregnated carbon contact, the life of the copper contact wasless than when used with the carbon contact without cadmiumimpregnation. Upon, using a copper contact having cadmium inserted inits face in place of the copper contact for cooperating with the cadmiumimpregnated carbon contact, the switch has continued in commercialoperation for over a year without appreciable wear on the contacts.

A feature of the invention is the use of cadmium as an insert in ametallic contact.

A second feature of the invention is a simple and economical method ofmanufacturing the contact involved in this invention.

A third feature of the invention is the -provision of a pair ofcontacts, one contact/having a cadmium insert and the other contactbeing of carbon impregnated with cadmium.

Other features and advantages will be apparent.

from the following description and appended claim.

The invention will be described by way of iilustration in connectionwith a switch adapted to open and close an electric circuit.

In the drawing: I

Figure 1 is a side view of a switch having contacts embodying theinvention:

Figure 2 is an enlarged view of the face of the movable contact shown inFigure 1;

Figure 3 is a section taken along the line 2-4 of Figure 2;

Figure 4 is a view of the face of another style of contact in accordancewith the invention: and

Figure 5 is a section taken along the line 5-8 of Figure 4.

Referring to the drawing, a switch I I embodyingthe present invention.is mounted on an insulating panel l2. Switch ll upon energization anddeenergization of a magnet coil I2, is arranged to attract and releasean armature I4 and a switch arm i5 secured thereto. A movable contacti8, carried by arm and insulated therefrom by a bushing i1, is adaptedupon movement of the arm to cooperate with a fixed contact It in themaking and breaking of an electric circuit. A spring between arm l5 andbushing ll acts to cushion the closing movement of the contacts. Fixedcontact 18, clamped in a holder 2i secured to panel 12, is made ofcarbon impregnated with cadmium.

.Movable contact l8, shown enlarged in Figures 2 and 3, consists mainlyof an integral head 22 and stem 23 made of copper. Stem 28 is suitablymachined for accommodating various necessary electrical connections.Head 22 is provided with an undercut recess 24 of dovetail section, inwhich a cadmium insert 25 is fixedly secured.

Insert 25 covers the greater part and is flush with a contacting surface26. Insert 25 is formed in head 22 of contact it by pouring moltencadmium into recess 24, with the contact cold, the copper walls of therecess being at the time relatively clean and free of oxide. The contactis then heated to the melting point of cadmium. This heating processcauses the cadmium to adhere or bind to the copper in much the samemanner as solder to a cleaned and tinned surface. Upon cooling thecadmium insert is finished flush with surface 28.

As previously stated. contact It consists of carbon impregnatedwithcadmium. When both contacts are of metal there is a possibility thatthey might fuse or freeze together due to arcing. i

It has been found that by using a contact of carbon against one of metalthe possibility of freezing together is eliminated. The use of a carboncontact impregnated with cadmium. such as contact l8, combines thenon-freezing feature of carbon with the long wearing feature of cadmium.

Head 22 may contain more than one cadmium insert and these inserts maybe of different anchoring shape. One such variation is shown in Figures4 and 5, where head 22 has a plurality of cadmium inserts 2! embeddedtherein in apertures 28 of screw thread section. Inserts 21 are formedand secured in head 22 in a manner as previously described for insert25.

What is claimed is:

In an electric switch, a copper contact with a cadmium insert embeddedtherein, said insert covering a portion of the contacting face of saidcontact and being flush with said face, and a carbon contact impregnatedwith cadmium for cooperating with said copper contact.

RAYMOND ALONZO WAITE.

